Cobalt‐hardened gold electrodeposits have been thermally oxidized under dry oxidation conditions in the temperature range 150°–250°C. Auger depth profiling and ESCA are employed to characterize the surface films as a function of time and temperature. Below 175°C, only is observed, as confirmed by ESCA. Above 175°C, growth is observed to decrease substantially and is qualitatively related to the recrystallization phenomena of the gold deposit. In this same temperature range, potassium evolution becomes significant. ESCA and quantitative Auger indicate that the potassium may be in the form of . A model was developed using a time‐of‐arrival approach to characterize potassium film growth. Approximate calculations give a diffusion coefficient for potassium through gold of at 200°C. This process is simply activated and has an energy of 1.25 eV. The source of potassium was speculated to be from possible decomposition of cyanide compounds trapped in voids or inclusions distributed uniformly in the gold deposit.